Recently, it has been perceived that the earth is in a state of warming and it has been hypothesized that the cause of this warming is human activity. The primary human activity attributed to the warming condition is the burning of fossil fuels. The burning of fossil fuel produces carbon oxides, primarily carbon dioxide (CO2), which is a most prevalent greenhouse gas, second only to water vapor. Data indicates that the CO2 level has increased by about 100 ppm (from about 280 to about 380 ppm) since the beginning of the Industrial Revolution. Greenhouse gases are those gases present in the earth's atmosphere that attenuate the loss of heat into outer space, thereby affecting global temperatures. Although essential to maintaining habitable temperature, an excess of greenhouse gases can raise the temperature of a planet.
Because of the desire to avoid additional warming, treaties and various strategies have been constructed in an attempt to control the anthropogenic sources of CO2. The efforts to maintain CO2 levels contradict the needs of a growing population, particularly where a greater proportion of the population is becoming more technically advanced. In attempts to combat this problem, the use of alternate energy sources has been encouraged and subsidized to reduce CO2 emissions. Although means such as solar, wind, geothermal, tidal, and hydroelectric sources do not generate greenhouse gas emissions, in many cases their reliability and accessibility do not allow dependence on such methods. An alternate method that does not generate CO2 is nuclear energy, although numerous barriers to greater implementation in some parts of the world exist. Although reliable and accessible for many activities, direct uses of any of these non-emitting alternates may not be appropriate for modern transportation needs, for example automotive, where a fluid fuel remains desirable.
A fuel that does not generate carbon oxides is hydrogen. Upon its combustion, hydrogen forms only water. The goal of a hydrogen economy has been envisioned where much research has been directed to fuel cells, storage systems, distribution networks and generation. Presently, hydrogen generation is considered by many to be cost ineffective. At the present time, hydrogen is most economically produced from hydrocarbons, where hydrogen can be generated from natural gas at approximately 80% efficiency. A primary or exclusive step is the steam reforming of natural gas where steam (H2O) reacts endothermically with methane (CH4) to yield H2 and carbon monoxide CO at high temperatures (700-1100° C.) which are generated by the burning of natural gas. Generally in a subsequent step additional hydrogen is recovered by the exothermic water gas shift reaction where the CO from the steam reforming process undergoes transformation at about 130° C. to produce H2 and CO2. Hence, hydrogen generation in this manner can generate more CO2 than does directly using the natural gas as a fuel. Hydrogen can also be formed biochemically, but prototype reactors using sulfur deprived algae reactors have produced hydrogen at only 7 to 10% efficiencies.
Direct electrolysis of water can produce hydrogen with efficiencies of about 25% without the formation of greenhouse gases. However, the electricity consumed is typically more valuable than the hydrogen produced and this mode of generation is not widely used. The electrolysis at very high temperatures has been carried out at the laboratory scale where the efficiency of electrolysis is increased to about 50%. The high temperature electrolysis (HTE) process is generally considered to be viable by combination with a nuclear heat source, as other non-chemically generated high-temperature heat sources are not considered consistent enough to justify the capital costs of HTE equipment. Even using nuclear heat sources, only prototype Generation IV nuclear reactors can operate at the temperatures (859 to 1,000° C.) identified for economical hydrogen production. No Generation IV nuclear reactors are anticipated before the year 2030. Hence, a sufficiently efficient generation of hydrogen without generation of carbon oxides is not anticipated to be economical for at least twenty years.